[Dr. Bellevue Column 73.] Why is Botox vulnerable to heat?

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Why is Botox vulnerable to heat?

Have you ever heard that Botox is weak against heat? Botox is indeed sensitive to heat. The reason is that its main ingredient, botulinum toxin, is made of protein. Proteins undergo a chemical change called denaturation when exposed to temperatures above a certain level. Botulinum toxin, the main ingredient in Botox, inhibits the release of a neurotransmitter called acetylcholine at nerve endings. Since acetylcholine is a substance that triggers muscle contraction, injecting Botox temporarily paralyzes the movement of specific muscles, helping improve wrinkles or reduce muscle volume.

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This effect of Botox works through a complex process in which the botulinum toxin protein binds to specific receptors on certain nerve cells, enters the cells, and breaks down the protein complex involved in neurotransmitter release (the SNARE complex). Proteins have their own unique three-dimensional structure, and this structure is very important for their function. When exposed to external factors such as strong heat, strong acids, strong bases, or organic solvents, the weak bonds that maintain the protein’s three-dimensional structure are broken, causing the structure to unravel or become tangled. This is called protein denaturation. When denaturation occurs, the protein loses its original biochemical activity.

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A simple example is when hair is burned or damaged while styling with a hair dryer or flat iron, which also corresponds to protein denaturation. The main component of hair is a protein called keratin. This protein consists of many amino acids forming polypeptide chains, and those chains create a stable structure through various bonds such as hydrogen bonds and disulfide bonds. At a moderate temperature (about 150–200℃), hydrogen bonds temporarily break and then reform, and this principle is used to change the shape of hair.

Protein denaturation: Why does hair get damaged when using a hair dryer at high temperatures?

However, when high heat continues or when exposed to very high temperatures above 230℃, the secondary and tertiary structures of keratin protein are permanently destroyed, the alpha-helix structure changes to a beta-sheet structure, and even disulfide bonds are broken, leading to protein denaturation. During this process, hair loses elasticity and becomes brittle or splits; in severe cases, it may burn, turn black, or break. In other words, hair burning at high temperatures can be explained by the same principle as denaturation, in which protein loses its original structure and changes its properties due to heat.

To explain briefly why Botox is vulnerable to heat, it comes down to the structural characteristics of proteins and heat-induced denaturation. The main ingredient in Botox is botulinum toxin type A, which is composed of a 150 kDa protein complex. To maintain its tertiary structure, proteins rely on weak bonds such as hydrogen bonds, hydrophobic interactions, and ionic bonds, and heat destroys these bonds, causing protein denaturation.

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● Mechanism of Botox denaturation by heat

1. Disruption of hydrogen bonds

The functional activity of Botox depends on a specific tertiary structure of the protein, especially the enzymatic active site of the light chain. At temperatures above 65°C, hydrogen bonds begin to break and the protein structure starts to unravel, and at 85°C it is completely denatured within 5 minutes. During this process, the active site responsible for breaking down the SNAP-25 protein is lost. If the three-dimensional structure of the botulinum toxin protein is altered, it may not bind properly to receptors on nerve cells, or the active site that breaks down the SNARE complex inside the cell may be damaged, causing it to lose its original function. It is like a key being deformed so that it no longer fits the lock. At extreme high temperatures, the protein may also break down into smaller fragments. Botulinum toxin that has been broken down this way can no longer produce a nerve-paralyzing effect.

2. Weakening of hydrophobic interactions

Botulinum toxin has a dual-chain structure consisting of a heavy chain (nerve cell target recognition) and a light chain (enzymatic activity). Heat interferes with the interactions between hydrophobic amino acid residues, causing the two chains to separate, which leads to a loss of nerve cell targeting ability.

3. Aggregation

Denatured proteins expose hydrophobic regions and aggregate with one another to form insoluble clumps. These aggregates may carry a risk of causing microembolism in blood vessels when injected, and the therapeutic effect is completely lost. Botulinum toxin, whose protein molecules have clumped together at high temperatures, cannot spread properly at the injection site and has reduced absorption, making it difficult to achieve an effect. It is similar to powder clumping together and not dissolving well in water.

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The paradox of heat resistance

Interestingly, Botox shows heat resistance compared with ordinary proteins. This is because accessory proteins (complex proteins) protect the toxin. However, prolonged exposure to high temperatures eventually reaches the limit of this protective mechanism as well. For example, when stored above 25°C for more than two weeks, activity decreases by 15%, and in a body-temperature environment of 37°C, efficacy drops by more than 50% within 24 hours.

Botox in refrigerated storage

Actual clinical impact

• Need for refrigerated storage: The manufacturer recommends storage at 2–8°C, and freezing is prohibited because it can destroy the protein structure. Refrigerated storage (2–8°C) is the rule, so leaving the product at room temperature for a long time or exposing it to high temperatures may reduce its effectiveness. Some products may become even less stable after dilution, so it is important to use them within the specified period.

• Post-procedure care: If the injection site is exposed to increased body temperature (such as in a sauna or during vigorous exercise), increased blood flow may cause Botox molecules to spread, leading to paralysis in unintended areas. There may also be a feeling of heat or inflammation at the treatment site, so cold compresses are recommended. Direct exposure to strong sunlight may also cause denaturation of the Botox protein, so it is important to apply sunscreen carefully. Strong massage of the treatment area should be avoided because it can cause uneven spread of Botox and generate heat.

Because of this heat sensitivity, Botox is manufactured in single-use vials and should be used immediately after opening. Injecting denatured Botox also increases the risk of an immune response (antibody formation), so heat management is essential for both treatment effectiveness and safety.

That’s all for today.

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